Petrol Overflow Pipe Query?

[Fat Bert]

Noticed a small patch of "damp" under the bike this afternoon.

First thought was oil leak. 

But its petrol - looks and smells like quality Esso!

Def coming from one of the 3 oveflow pipes

The tank is only 1/3 full

The bike has stood in the blazing sunshine all day.

Never noticed it before and cooler garage floor shows no evidence

Thoughts? 

[baudbish]

My understanding is that they are not 'overflow' pipes but 'breather' pipes.  If your bike is sat in direct hot sunlight then the petrol will obviously 'vape' off within the fuel tank and the only exit is via the 'breather' pipe where it will condense and then may drip out.  Better this that have a dangerous build-up of vapourised gas (under pressure) within the fuelk tank.

[__Ray__]

There are 2 hoses from the tank. 1 is the breather to prevent a vacuum in the tank witch lead to stop of fuel supply to the engine and the other is an overflow to prevent the bud up of pressure and more important to prevent gasoline leaking trough the cap and ending up on the hot engine.